All components tested now including, ADC, MPU9250 gyros and accelerometer, voltage regulators, servo control, buttons and flash memory. I finally soldered the flash memory in the incorrect footprint by bending the legs, it took some time but it works.
As I commented with @Mike Szczys , today I performed the static tests in order to ensure the structural integrity of the gimbal. The test was a success with some observations to be considered.
The test bench was quite improvised and low cost but worked nicely for the purpose of the test.
The test reached 12.2 kg without any strange noise.
The servos worked smoothly after the test.
The plastic structure recovered totally the initial shape and there is no sign of permanent deformation.
The inner rings had no visible deformation.
However, the external structure deformed significantly, but the supporting is no representative of the real conditions. I will perform finite element simulation in order to study the deformation of the body tube and make sure that deformations are reasonable and there is no risk of local buckling. Local reinforcements will be introduced to the zone if shown to be necessary.
Also, the bearing of the outer ring slightly moved out of the hole. I will glue it with epoxi to make sure it stays where it should. Maybe this can be avoided with some geometry changes if I ever re-design the gimbal.